extract gpg functionality to lib class

app/models/gpg_key.rb

@@ -33,12 +33,8 @@ class GpgKey < ActiveRecord::Base
   private
 
   def extract_fingerprint
-    import = GPGME::Key.import(key)
-
-    return if import.considered == 0
-
     # we can assume that the result only contains one item as the validation
     # only allows one key
-    self.fingerprint = import.imports.first.fingerprint
+    self.fingerprint = Gitlab::Gpg.fingerprints_from_key(key).first
   end
 end

lib/gitlab/gpg.rb

+module Gitlab
+  module Gpg
+    extend self
+
+    def fingerprints_from_key(key)
+      using_tmp_keychain do
+        import = GPGME::Key.import(key)
+
+        return [] if import.imported == 0
+
+        import.imports.map(&:fingerprint)
+      end
+    end
+
+    def using_tmp_keychain
+      Dir.mktmpdir do |dir|
+        @original_dirs ||= [GPGME::Engine.dirinfo('homedir')]
+        @original_dirs.push(dir)
+
+        GPGME::Engine.home_dir = dir
+
+        return_value = yield
+
+        @original_dirs.pop
+
+        GPGME::Engine.home_dir = @original_dirs[-1]
+
+        return_value
+      end
+    end
+  end
+end

spec/lib/gitlab/gpg_spec.rb

+require 'rails_helper'
+
+describe Gitlab::Gpg do
+  describe '.fingerprints_from_key' do
+    it 'returns the fingerprint' do
+      expect(
+        described_class.fingerprints_from_key(GpgHelpers.public_key)
+      ).to eq ['4F4840A503964251CF7D7F5DC728AF10972E97C0']
+    end
+
+    it 'returns an empty array when the key is invalid' do
+      expect(
+        described_class.fingerprints_from_key('bogus')
+      ).to eq []
+    end
+  end
+
+  describe '.add_to_keychain' do
+  end
+end

spec/spec_helper.rb

@@ -143,14 +143,8 @@ RSpec.configure do |config|
   end
 
   config.around(:each, :gpg) do |example|
-    Dir.mktmpdir do |dir|
-      original_dir = GPGME::Engine.dirinfo('homedir')
-
-      GPGME::Engine.home_dir = dir
-
+    Gitlab::Gpg.using_tmp_keychain do
       example.run
-
-      GPGME::Engine.home_dir = original_dir
     end
   end
 end